Double disc eddy current loud-speaker



Oct. 14,

2 Sheets-Sheet l 1947. w.- K. M IVER DOUBLE DIS C- EDDY CURRENT LOUD-SPEAKER Filed Jan. 1, 1945 F" .L A? g Inventor- William K. Mclver,

H is Attorne Oct. 14, 1947. w. K. M IVER 2 DOUBLE DISC EDDI CURRENT LOUD-SPEAKER I Filed Jan. 1, 1945 zsheets-she t Inventor: William K. NcIvev,

Patented Oct. 14, 1947 DOUBLE DISC EDDY CURRENT LOUD-SPEAKER William K. McIver, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Application January 1,1945, Serial No. 570,817

4 Claims.

My invention relates to sound reproducing apparatus and particularly to loudspeakers of the type which provide mechanical amplification of relatively low power electric energy variations.

It is an object of my invention to provide a loudspeaker of the mechanical type which is of rugged construction and which provides high amplification with minimum distortion.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings in which Fig. 1 is a side elevation view, partly in section, of the mechanical loudspeaker embodying my invention; Fig. 2 is a sectional view of the loudspeaker shown in Fig. 1 taken on the line 2-2 of Fig. 1; Fig. 3 is a perspective view, partly in section and partly exploded, showing the mechanism of Figs. 1 and 2 removed from its casing; and Fig. 4 is a circuit diagram of a pushpull amplifier suitable for driving the loudspeaker shown in Figs. 1, 2, and 3.

Briefly, the loudspeaker illustrated in the drawings comprises a pair of metal disks rotatably mounted on spaced parallel axes in a suitable elongated frame. The frame is resiliently mounted on a supporting structure or casing and is constrained to move only in the direction of its longitudinal axis at right angles to the axes of the disks. The disks are driven at very high speed in opposite directions, and a pair of electromagnets excited in push-pull relationship are secured on the support and arranged to cooperate with the disks to produce vibration of the frame in accordance with the energization of th electromagnets. The frame is connected to drive loudspeaker diaphragms connected to the ends of the frame. The disks are driven through a herringbone type gearing so that lateral forces are balanced and the entire mechanism is balanced so that vibration is minimized and the diaphragms are actuated only by excitation of the electromagnets. The electromagnets are arranged to produce drags proportional to the signal excitation and a drag is produced in each disk near its periphery. High amplification is produced mechanically by this arrangement.

Referring now to the drawings, the loudspeaker illustrated in Figs. 1, 2, and 3 comprises a casing I having a top cover 2 and arranged to form a sump in its lower portion for holding a body of lubricating oil or other liquid 3. Two sound reproducing diaphragms 4 and 5 respectively are mounted outside the casing at either end thereof. Both diaphragms are connected to an elongated frame or rod 6 which is mounted on resilient supports of spiders l and 8 adjacent the speakers 4 and 5 respectively. The spiders are arranged to constrain the rod for movement substantially only in the direction of the longitudinal axis of the rod. The spiders are mounted on supports 9 and I0 respectively which are secured to the end walls of the supporting casing l. The rod 6 is connected to drive th diaphragms 4 and 5 by means of bars II and i2 which are threaded into the ends of the rod and extend through bosses 9a and Illa at the ends of the casing. The bars II and 12 are provided with stepped down threaded portions for retaining collars Ila and [2a in position to engage the bosses 9a and "la and positively limit the maximum longitudinal movement of the frame 6.

The diaphragms 4 and 5 are driven by the frame 6 which is vibrated longitudinally in accordance with the sounds to be reproduced. In order to produce the longitudinal vibration of the frame, a pair of metal disks l3 and I4 are mounted in the frame for rotation on horizontal shafts l5 and I6 normal to the longitudinal axis of the frame. Th shafts l5 and I6 are mounted in ball bearings I1 and IS in the frame 6. As shown in Fig. 2, the shaft I5 is provided with pinion gears 19 and 20 on either side of the disk I3. These pinions are driven by gears 2| and 22, respectively, which are mounted on a common shaft 23 driven by a motor 24 located outside the casing and connected to the shaft by a flexible coupling 25. The shaft 23 is mounted in ball bearings 26 and 21 in the walls of the housing I.

The gearing for driving the disk I4 is the same as that for driving the disk l3 and includes pinions on either side of the shaft l6, only one of which is shown as indicated at 28, and driving gears 29 and 30; the gear 29 meshes with the pinion 28, and the gear 30 meshes with the other pinion which cannot be seen in the drawing. The gears 29 and 30 are secured to a shaft 3| which is mounted in ball bearings (not shown) in the walls of the supporting casing l. The gears 29 and 30 mesh with th gears 2| and 22, respectively, and are thereby driven by the motor 24 at the same speed as the gears 29 and 30 but in the opposite direction. It is thus apparent that 3 the disks [3 and [4 are rotated in opposite directions and at the sam speed. The motor 24 is selected to operate at constant speed so that the disks are driven at the same speed throughout th operation of the loudspeaker.

The gears and pinions preferably are provided with helical teeth, each pair of gears and pinions having teeth inclined in opposite directions to balance lateral forces on each of the shafts, and the pairs of gears and pinions thus constitute a gearing of the herringbone type. In order further to increase the smoothness of operation of the gearing, the teeth in the two gears or pinions forming each pair preferably are staggered with respect to one another.

In order to drive the frame 6 in accordance with the sounds to be reproduced, a pair of electromagnets 32 and 33 are mounted adjacent the disks l3 and M, respectively; these magnets are supported on arms 34 and 35 secured between the walls of the casing 1. Each electromagnet comprises a core having an air gap in which the associated disk rotates. As clearly shown in Figs. 2 and 3, the electromagnet 32 comprises a magnetic core 85 having an air gap within which the disk l3 rotates and provided with exciting coils 3'! one on either leg of the core 36. The electromagnet 33 comprises a similar core 38 and coils 39. It will readily be apparent that when one of the electromagnets is energized it will produce a drag on the metal disk rotating in the air gap of the core structure due to the setting up of eddy currents in the disk. The drag on the disk opposes rotation of the disk and produces torque exerting a force on the disk shaft tending to displace the frame 6 on which the shaft is mounted. By energizing the electromagnets with electrical energy varying in accordance with the sounds to be reproduced, the frame will be vibrated in accordance with the sounds and will drive the diaphragms 4 and 5.

The electromagnets 32 and 33 are energized in push-pull relationship, a suitable circuit for this purpose being shown in Fig. 4. The amplifier comprises electron discharge devices 46 and 4! having the windings of the two electromagnets 32 and 33 connected in series with a source of direct current M in the respective anode-to-cathode paths of the devices 49 and il. The devices 26 and ii include control electrodes 46 and 67, respectively, on which the signal to be reproduced is impressed by means of the secondary winding of the transformer 63, the primary of the transformer :8 being energized through a suitable signal generating apparatus 43 in accordance with sounds impressed on a microphone 52. The electromagnets 32 and 33 are thus energized in accordance with the opposite halves of the signal wave. The drags produced on the disks l3 and M are thus produced alternately by the opposite halves of the signal wave so that the drags are produced on the disks in push-pull relationship. It will therefore be apparent that since the disks are rotated in opposite directions the frame 5 will be driven in one direction when the magnet 32 is energized and in the opposite direction when the magnet 33 is energized. This is the condition necessary for reproducing the signals applied in push-pull relationship. The diaphragms 4 and 5 are, therefore, driven by the frame 6 to reproduce the signals impressed on the electromagnets of the mechanical amplifier through the push-pull electronic amplifier circuit of Fig. 4.

The frame 8 is preferably made of a light material such as an aluminum or magnesium alloy,

and the disks [3 and H are constructed of similar material to minimize the inertia of the moving parts of the assembly. The disks l3 may be constructed of any suitable material having good electrical conductivity, light metals being preferable to avoid high inertia effects. In order to insure adequate lubrication and also substantial cooling of the gearing, the gears 2|, 22, 29, and 30 are arranged to be partially submerged in the oil in the bottom of the casing I, and oil is thereby picked up and thrown about the interior of the casing and over the driving mechanism. Obviously, suitable shielding may be provided should it be desired to protect any portions of the apparatus from the splashing lubricant.

A loudspeaker constructed as shown in the drawings may be arranged to provide mechanical amplification such that the power output is of the order of 300 times the input. For example, a mechanical amplifier having disks six inches in diameter rotated at a constant speed of 24,000 R. P. M. may be made to produce a 1,000 watt output when excited by a push-pull amplifier having an output of the order of 3 watts. It is readily apparent that this provides a simple and effective arrangement for producing high output for loudspeakers without the necessity of providing high power electronic amplifiers.

Although I have illustrated a specific embodiment of my invention, other arrangements and applications will occur to those skilled in the art. I do not, therefore, desire my invention to be limited to the particular construction illustrated and described, and I intend by the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A sound reproducing apparatus comprising a support, a frame, resilient means for mounting said frame on said support and for constraining said frame to move substantially only in a predetermined direction, a pair of metal disks mounted on said frame for rotation about axes at right angles to the direction of movement of said frame, means for rotating said disks in opposite directions at constant speed, a sound reproducing diaphragm connected to be driven by said frame, and means including a pair of electromagnets mounted on said support and spaced from said disks for producing drags on said disks proportional to the sound vibrations to be reproduced, one of said magnets being arranged adjacent one of said disks and the other of said magnets adjacent the other of said disks, and means for energizing said magnets in push-pull relationship in accordance with sounds to be reproduced whereby said frame is vibrated to drive said diaphragm and reproduce said sounds.

2. A sound reproducing apparatus comprising a support, a frame, resilient means for mounting said frame on said support and for constraining said frame to move substantially only in a predetermined direction, a pair of metal disks mounted on said frame for rotation about axes at right angles to the direction of movement of said frame, each of said disks having a pinion gear concentric therewith, means including a pair of meshed driving gears one in mesh with one of said pinions and the other with the other of said pinions for rotating said disks at constant speed and in opposite directions, a sound reproducing diaphragm connected to be driven by said frame, a pair of electromagnets mounted on said support one adjacent and spaced from one of said disks and the other adjacent and spaced from the other of said disks, and means for energizing said electromagnets in push-pull relationship in accordance with sound vibrations to be reproduced whereby said frame is vibrated to drive said diaphragm in accordance with such vibrations.

3. A sound reproducing apparatus comprising means providing a support and a closed casing, a body of liquid lubricant in the lower portion of said casing, a frame in said casing, resilient means for mounting said frame on said support and for constraining said frame to move substantially only in a predetermined direction, a pair of metal disks mounted on said frame for rctation about spaced axes at right angles to the direction of movement of said frame, a pinion gear connected to each of said disks coaxially therewith, means including a pair of meshed driving gears one in mesh with the pinion of one disk and the other with the pinion of the other disk for rotating said disks at constant speed and in opposite directions, said driving gears being partially submerged in said lubricating liquid, a sound reproducing diaphragm connected to be driven by said frame, a pair of electromagnets mounted on said support one adjacent and spaced from one of said disks and the other adjacent and spaced from the other of said disks, and means for energizing said electromagnets in push-pull relationship in accordance with sound vibrations to be reproduced whereby said frame is vibrated to drive said diaphragm in accordance with such vibrations,

4. A sound reproducing apparatus comprising a support, a frame, resilient means for mounting said frame on said support and for constraining said frame to move substantially only in a predetermined direction, a pair of metal disks mounted on said frame for rotation about spaced axes at right angles to the direction of movement of said frame, two pairs of pinion gears connected to said disks coaxially therewith, the pinions of one pair lying on opposite sides of one disk and those of the other pair on opposite sides of the other disk, means including two pairs of driving gears meshed with each other and with respective ones of said pairs of pinions for rotating said disks at constant speed and in opposite directions, said gears and pinions of each of said pairs having oppositely inclined teeth to constitute each pair a gear of the herringbone type for balancing lateral thrusts, a sound reproducing diaphragm connected to be driven by said frame, a pair of electromagnets mounted on said support one adjacent and spaced from one of said disks and the other adjacent and spaced from the other of said disks, and means for energizing said electromagnets in push-pull relationship in accordance with sound vibrations to be reproduced whereby said frame is vibrated to drive said diaphragm in accordance with such vibrations.

WILLIAM K. MCIVER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,961,286 Engholm et al June 5, 1934 1,866,361 Kuehni July 5, 1932 477,866 Hope-Jones June 28, 1892 1,035,577 Grace Aug. 13, 1912 1,696,303 Hutchison Dec. 25, 1928 FOREIGN PATENTS Number Country Date 458,287 Great Britain Dec. 16, 1936 

